1. Field of the Invention
This invention relates to a polarizer for controlling the state of polarization of microwave signal carrier modes in a waveguide. More particularly, this invention relates to a polarizer for optimum control of the state of polarization of a signal carrier waveguide dominant mode over a very wide bandwidth at microwave frequencies.
2. Description of the Prior Art
Since modern communication satellites have a life expectancy beyond seven years and since the beam coverage requirements for a particular satellite are constantly changing, there is a need for a certain amount of reconfigurability of antenna radiation characteristics in terms of the beam footprint on the earth's surface and the state of field polarization. Sometimes, satellites must be repositioned in orbit and as a result the radiated field polarization and beam footprint must be varied. Well-known frequency use techniques are employed to accomplish an efficient link utilization. It is also desirable to widen the bandwidth of operation for the links so that more communication traffic can be accommodated. A waveguide polarizer is one of the key components used in both satellites and ground stations for manipulation of radiated and/or received field polarization and for manipulation of beam footprint. While techniques to achieve these manipulations employing waveguide polarizers are well-known, previous polarizers are incapable of achieving acceptable electrical characteristics for use in satellite communication systems; or, they are structurally too complex and therefore extremely expensive; or, they are structurally complex and cannot be designed accurately using computerated design and analysis procedures; or, they are extremely difficult to construct accurately; or, they require conventional circular waveguides to be connected at the input and output ports; or, the insertion loss is unacceptably high; or, they have an inconvenient physical layout; or, they are not sufficiently reliable to be used in satellites; or, they require the use of transition sections at the input and output ports; or, they are unable to control the phase dispersion slope for more than one hand of polarization; or, they achievable bandwidth is not able to meet many practical requirements. Some of these prior art polarizers are shown in the drawings and discussed in relation thereto.